This invention relates to an autonomous vehicle arrangement and methods for controlling autonomous vehicles.
Many efforts to provide autonomous vehicles have been made. As used herein "autonomous vehicle" means a driverless vehicle that moves independently from a point of origin to a destination, with or without human passengers. Autonomous vehicles must be distinguished from vehicles that are remotely controlled by wire or radio so that a person outside of the vehicle continues to take responsibility for the movement.
Autonomous vehicles have already reached such a standard in the field of materials transport that they have found a variety of industrial applications. Thus, autonomous vehicle arrangements have been proposed in which a guide cable or control wire is disposed along a route and the vehicle is guided along the guide cable. When a specific signal is transmitted to the guide cable, the presence of the signal is detected by a pickup coil installed on the vehicle, and the vehicle moves along the guide cable route, and any deviation from the prescribed route is determined with the aid of the guide cable. In a further conventional arrangement for an autonomous vehicle system, an optically reflecting tape, for example an aluminum or polyvinyl tape, is placed along the surface of the travel path instead of a guide cable, and a light projector and a photodetector are mounted on the autonomous vehicle. The light emitted by the projector is reflected by the tape and received by the photodetector and, in this way, the unmanned vehicle is guided along the reflecting tape. A disadvantage of the conventional autonomous vehicle arrangements is that desired vehicle routes cannot be freely chosen, but instead must be installed in advance.
U.S. Pat. No. 5,229,241 discloses an autonomous transport vehicle containing an image processing unit that photographs the environment in the forward direction of the vehicle and processes the photographed image, a position finding unit that calculates the position of the vehicle in an absolute coordinate system on the basis of information obtained from a wheel speed sensor, a gyroscope and the like, a drive unit that includes the vehicle's steering, gas pedal, brake system, turn signals and the like as well as actuators to operate these devices including the associated servo drivers, a unit in which are stored site plan data and map data regarding a destination and information defining a route, a travel control unit that controls the drive unit with the aid of the information obtained from the image processing unit, the position finding unit, and the information storage unit in such a way that the vehicle drives to a final destination, and a user interface for entry of information relating to a destination, i.e., a variety of destination points that are defined on the route by the travel control unit, and for display of the image obtained from the image processing unit as well as other information.
For this purpose, the image processing unit includes two cameras located at the front of the vehicle which record a stereo image of the environment. The spatial image photographed by the two cameras is converted through an inverse transformation in an image processing unit into a plane image. For instance, the image processing unit identifies a pair of white guide lines painted along the travel path, a travel path side boundary, a center line and the like, and measures the length of the lines in relation to the vehicle. In particular, through the sensing of the white lines on the travel path, the spatial relationship between the vehicle and the travel path is calculated, i.e. the distance of the vehicle from the white line on the left and/or right side of the travel path, the angle between the forward direction of the vehicle and the travel path, and the like and, in the case of a curved travel path, the direction of the curve is determined at half the distance of the travel path. In addition, the distance of the vehicle from an intersection is determined by detecting and measuring the intersection point of the white lines before the intersection is reached.
The image processing unit further contains an ultrasonic sensor, a laser radar and the like for detecting obstacles located on the travel path in front of the vehicle and to the side of the vehicle, as, for example, a vehicle traveling in front, a protective barrier, and the like, and for transmitting the corresponding information to a position finding unit of the vehicle. The position finding unit includes two wheel speed sensors that are located on the left and right rear wheels of the vehicle, a processing unit that receives and processes the output signals of the two wheel speed sensors, and a calculation unit for calculating the location of the vehicle in global coordinates. The wheel speed sensors detect the rotation of the vehicle's rear wheels and generate several thousand pulses per revolution for each wheel. When a difference is found in the number of pulses generated for the individual wheels, this means that there is a difference in the distance covered by the corresponding wheels, and this difference in the distance covered forms the basis for determining the curvature of the section of travel path being traveled by the vehicle. In addition, the distance covered by both wheels indicates the distance traveled by the vehicle. The path of the vehicle can thus be calculated on the basis of the sequences of data provided by the wheel speed sensors. In particular, information relating to the location and position of the vehicle at a specific point in time, i.e. information regarding the vehicle's location and direction of travel in an X-Y coordinate system, can be derived.
If the vehicle location is known at the start of the trip, the current location of the vehicle during the trip can be monitored continuously, since the wheel speed data is processed sequentially. Because the errors in the determination of vehicle location accumulate, the measurement errors increase with increasing distance traveled by the vehicle. For this reason, a gyroscope is provided so that the position in an absolute coordinate system can be determined with high accuracy. However, such an autonomous vehicle for material transport is only suitable for use in defined areas, such as manufacturing halls or an industrial plant, where nearly identical external conditions prevail.
In addition, German Offenlegungsschrift No. 41 24 654 describes a method for continuous and automatic vehicle orientation on a travel path in which an automatic vehicle guidance system is provided for better utilization of transport capacity of traffic routes. In this method, a television camera that is mounted on the vehicle as high as possible above the travel path continuously transmits digitized image sequences at the video rate to a computer system with a program for special signal processing and interpretation in the vehicle. In this method, generic street models and simple, generic, dynamic models for the vehicle movement are utilized in order to be able to use previously incorporated travel path recognition and relative vehicle position recognition to evaluate the next image. For this purpose, three partial models are combined. Monocular image data of only the last image are analyzed with recursive estimation methods to determine street parameters and the vehicle's location with respect to the streets. In this way, a spatial projection is produced in the computer of the current street path in the area of prediction.
U.S. Pat. No. 5,610,815 discloses an autonomous vehicle, specifically for use in open-pit mining, that has a first position finding system based on GPS (Global Positioning System) and a second IRU (Inertial Reference Unit) positioning system based on a gyroscope, and the data from these systems are computed together in a third position finding system for accurate position determination. In addition, the autonomous vehicle contains a navigation system by which the vehicle can be guided on predefined or dynamically determined routes. The navigation system monitors the current position as well as the mechanical vehicle components such as brakes, steering and motor, and can shut down the vehicle if serious malfunctions occur. Moreover, the navigation system includes an obstacle detection device in order to detect objects located on the planned route and, if necessary, to steer an avoidance course or stop the vehicle. For this purpose, an infrared laser scanner in single line mode is placed on the roof of the vehicle, where the scanning angle is between 10.degree. and 30.degree.. The scanning beam is oriented in such a way that it does not reach the ground. This ensures that detected obstacles are not the result of irregularities in the ground. For detection of ground irregularities, a second laser scanner in multiple line mode is aimed at the ground at a specific angle. That angle is selected in such a way that obstacles are detected at a distance corresponding to the vehicle stopping distance so that the vehicle can be stopped in time before reaching the obstacle.
This autonomous vehicle designed especially for open-pit mining is very advanced in the areas of position finding and route generation, but does not take into account important aspects for the use of an autonomous vehicle in traffic on public roads. Thus, for example, a limitation of the field of view to be evaluated is not possible in street traffic, since vehicles on merging streets must be detected in advance in a timely manner, on the one hand in order to adapt the driving behavior to the applicable traffic regulations, and on the other hand also to be able to react preventively to improper behavior of a vehicle on a merging street. This illustrates that, while basic structures of the known autonomous vehicles are generally suitable in part, as, for example, the position finding system, others are inadequate in the known art.